1. Field of the Invention
The present invention relates to a brake adjustment indicator and, more particularly, to a brake adjustment indicator for air disc and cam operated brakes for large trucks, trailers and the like.
2. Description of the Prior Art
For many years, it has been appreciated that there is a need to accurately determine whether brakes on trucks, trailers and other such vehicles, have worn to the point where adjustment is needed in order to maintain the brakes in good working order.
However, current braking systems are very difficult to inspect and, therefore, inspection of the systems may not be made as frequently as they should be due to the difficulty attendant with such inspection. Clearly, the potential hazardous condition shouldthe brakes of a vehicle be worn is readily apparent. Accordingly, attempts have been made to develop wear indicator devices which one can readily inspect. However, these devices have generally been rather cumbersome, and require extra, complicated components thereby making them costly, or use elements or component which can readily wear and, therefore, need replacement, or require access to the air chambers or brakes themselves and, therefore, special provisions, which are costly, are needed to make sure the brake components are not adversely effected.
The following are examples of devices having extra components which can readily wear. U.S. Pat. No. 2,644,549 to Cagle, which issued July 7, 1953 is directed to a brake disc wear compensating and indicating means which automatically takes up the clearance between a brake drum and the brake element in response to wear of the brake element by the action of a combined spring return means and an adjustable holding device which presses upon wear indicator means. Analogously, U.S. Pat. No. 3,018,852 to Stanton, which issued Jan. 30, 1962, is directed to a combination retracting mechanism and wear indicator. This indicator, like the indicating means in Cagle, is rather cumbersone and also uses springs. Further, U.S. Pat. No. 4,658,936 to Moseley, which issued Apr. 21, 1987, provides a brake temperature and wear indicator which uses a biasing means, such as a spring, to bias a probe having a thermocouple embedded within to press upon the pressure plate of a multi-disk brake assembly for an aircraft.
An example of a device which requires access to the brakes or air chambers for the brakes is U.S. Pat. No. 4,583,071 to Sebalos, et al., which issued Apr. 15, 1986, which provides a brake adjustment monitoring device for automotive vehicles. The device consists of a magnet adjustably secured to the shaft of the diaphragm within each air chamber.
Along these same lines, U.S. Pat. No. 3,298,466 to Ayers, Jr., et al., which issued Jan. 17, 1967, is directed to a brake wear indicator which consists of an extension of a spring. The spring is located in the housing for the brakes and the wall of the housing has an opening to permit the extension to pass therethrough. U.S. Pat. No. 4,279,214 to Thorn, which issued July 21, 1981, provides a brake wear indicator which is a sleeve that loosely fits over the push rod to the pneumatic actuator of the brakes. However, the sleeve has an outside diameter permitting it to be received in the aperture of the actuator housing which slidably receives the push rod. See also, U.S. Pat. No. 4,186,822 to Khuntia, et al., which issued Feb. 5, 1980, which provides a disk brake wear indicator in which a base is provided in the piston retracting mechanism which includes a spring. Through the base, which is plugged when not in use, a depth measuring device can be inserted to obtain a reading.
Also, see U.S. Pat. No, 4,356,897 to Urban, which issued Nov. 2, 1982, which provides a lining wear indicator for a disc brake. The indicator includes a pair of pins secured at their outboard ends to the respective radially outer ends of the bridge bar and extending axially inboard through aligned bases in the inboard web of the caliper of the brakes.
The only suggestion of an indicator device which neither employs springs which, after use or wear, can stretch and, therefore, need replacing, nor requires entry through the walls of the device to be measured, is U.S. Pat. No. 3,438,351 to Kirkwood, which issued Apr. 15, 1969. This patent, which is not directed to a wear or adjustment indicator for brakes of a vehicle, is directed to means for simultaneously indicating the spacing between two opposed attritioning elements and their condition of wear. Specifically, a rod is attached to the axially-adjustment element of a pair of axially-aligned attritioning elements. A slidable bracket is placed on the rod and the bracket includes a pointer. The pointer is adapted to move over a stationary scale to indicate the actual spacing between the attritioning elements when separated. There is also provided a second scale which is carried on the slidable bracket, and a second pointer fixed on the rod. This second pointer indicates on the second scale the amount of wear of the attritioning elements.
None of the above patents provide a wear indicator device for the brakes of a truck, trailer or the like which does not employ springs and also does not pierce or effect the housing of the brakes or air chamber for the brakes. Further, until the present invention, there was no wear indicator device for brakes of vehicles which requires only relatively simple and inexpensive components which can be readily mounted on the mounting bracket for the brakes and does not effect the housing of the brakes or the brake air chamber.